The characteristics of a given type of rope determine whether that type of rope is suitable for a specific intended use. Rope characteristics include breaking strength, elongation, flexibility, weight, abrasion resistance, and coefficient of friction. The intended use of a rope will determine the acceptable range for each characteristic of the rope. The term “failure” as applied to rope will be used herein to refer to a rope being subjected to conditions beyond the acceptable range associated with at least one rope characteristic.
The present invention primarily relates to the performance of rope when the rope fails due to excess tension loads. When a rope is subjected to excess tension loads, the rope fails over time in what will be referred to as a tension failure sequence. For the purposes of the following discussion, it will be assumed that a constant tension load is applied to the rope throughout the tension failure sequence. However, a rope of the present invention may be used in situations in which the tension load varies or is eliminated during the tension failure sequence.
The tension failure sequence varies from rope to rope and from environment to environment. In general, a rope or portion of a rope breaks when all of the fibers of the rope separate or break apart at a given location on the rope. If the fibers are all identical, it is conceivable that all of the fibers will break at the same time. Typically, however, individual fibers differ from each other based on such factors as manufacturing variations and wear on the fibers during use of the rope. Accordingly, when the failure sequence begins, the lower elongating fibers will break first, transferring the load to the remaining fibers. As the entire tension load is transferred to the remaining higher elongating fibers, these also begin to break. When all of the fibers have broken at a given location, the rope is broken.
In a conventional rope, the tension failure sequence typically begins with elongation of the rope. After a certain amount of elongation, the rope breaks, marking the end of the tension failure sequence. At the end of the tension failure sequence, the rope exceeds the acceptable range of elongation and eventually breaks. When the rope breaks, potential energy within the rope is converted into kinetic energy that can cause unpredictable movement of the ends of the rope on either side of the break.
The need thus exists for improved ropes that, when subjected to excess tension loads, fail in a controlled manner; the need also exists for systems and methods for controlling the failure of rope and for producing such improved ropes.